DESCRIPTION (Applicant's Description Verbatim): The goal of this project is to develop rapid, low-cost methods for determining regional blood flow in mammalian tissues and to make regional blood flow measurements more widely accessible to researchers through lower-cost and time-saving instruments. This research is based on the working hypothesis that the distribution of fluorescent microspheres injected into circulatory flow can be directly counted in compressed-tissue samples to determine regional blood flow. This technology would replace current indirect methods that estimate numbers of microspheres, that involve extensive handling of radioactive or caustic solutions, and that require expensive supplies and instrumentation. The precision and accuracy of compression-imaging methods for counting microspheres in tissues were evaluated during Phase I. Line-scan imaging offers rapid flow analysis with minimal sample handling at moderate cost. Photographic imaging, a lower-cost alternative, takes more time, but also greatly simplifies microsphere counting. The instruments and methods will be tested on tissue samples containing microspheres of up to four different fluorescent colors. The Fluorescent Microsphere Resource Center at the University of Washington will validate these methods against the well-established radioactive microsphere method. PROPOSED COMMERCIAL APPLICATION: This technology will replace current methods of estimating microspheres with instruments that directly count microspheres. Potential markets include the hundreds of laboratories currently using fluorescent microspheres and the large numbers of additional researchers utilizing the alternative radioactive- and colored-microsphere methods.